The surface of U-2.5% Nb alloy was hydrogenated by gas-solid reaction system. Hydrogen corrosion of U-2.5% Nb alloy was observed in situ using a stereomicroscope, and the composition and morphology of the alloy before and after hydriding were characterized by X-ray diffraction (XRD), laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). The results showed that the hydrogenation rate of U-2.5% Nb alloy was very high at 70℃ and hydrogen pressure was one atmosphere, and UH3 compound was formed after hydriding. The edge of the hydrogen corrosion point on the surface of the alloy was not smooth, but rather the nucleus was preferentially nucleated and protruded outwards. The mechanism of hydrogenation corrosion on the surface of U-2.5% Nb alloy is that the hydrogen corrosion rate of α-phase of niobium is higher than that of niobium γ1-2 phase and preferential hydrogen corrosion of α phose occurs, and hydrogen corrosion of γ1-2 phase occurred one after another and quickly grew up.